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Add a delay combinator.

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This commit is contained in:
Rob Rix 2015-09-18 15:42:53 -04:00
parent abb63b7c4d
commit 4f1181c51e
1 changed files with 6 additions and 0 deletions
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6
prototype/Doubt/Parse.swift
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@ -40,6 +40,12 @@ public func not<T>(parser: String -> State<T>?)(_ input: String) -> State<String
}
/// Delays evaluation of a parser.
public func delay<A>(thunk: () -> String -> State<A>?) -> String -> State<A>? {
return { thunk()($0) }
}
public func parseWhile(predicate: Character -> Bool)(_ input: String) -> State<String>? {
return input.characters.count > 0 && predicate(input.characters[input.startIndex])
? parseWhile(predicate)(input.from(1)).map { State(rest: $0.rest, value: input.to(1) + $0.value) } ?? State(rest: input.from(1), value: input.to(1))